In many conventional Cu wiring boards, an adhesion layer is provided between an insulating layer formed on a substrate and a Cu wiring layer formed on the insulating layer (for example, refer to Japanese Laid-Open Patent Application No. 2003-218516). The adhesion layer is provided to fix the Cu wiring layer so that the Cu wiring layer is not separated from the substrate.
A resin material is used as an insulating layer formed on a substrate in many cases. According to a type of a resin to be used, even an adhesion layer formed of CuN does not provide sufficient adhesion strength. If adhesion strength of the adhesion layer is insufficient, a separation may occur between the CuN adhesion layer and the resin insulating layer, which may result in separation of a Cu wiring layer together with the resin insulating layer. Thus, it is suggested to improve adhesiveness between the resin insulating layer and the adhesion layer by forming the adhesion layer by an NiCu alloy (for example, refer to Japanese Laid-Open Application No. 2009-188324).
However, even if an adhesion layer is formed by an NiCu alloy to improve adhesiveness between an insulating layer and an adhesion layer as suggested in the above-mentioned patent document, sufficient adhesiveness may not be obtained depending on a type of resin forming the insulating layer.